8
Relative Humidity Sensors (Space or Duct
Mounted)
The accessory space humidity sensor or duct humidity
sensor is used to measure the relative humidity of the air
within the space or return air duct. The RH reading is used
to control the Perfect Humidity
t
option of the rooftop
unit. For wiring distances up to 500 ft (152m), use a
3-conductor, 18 or 20 AWG shielded cable. The shield
must be removed from the sensor end of the cable and
grounded at the unit end. The current loop power for the
sensor is provided by the RTU Open controller as 24vdc.
Refer to the instructions supplied with the RH sensor for
electrical requirements and terminal locations. RTU Open
configurations must be changed after adding a RH sensor.
See below and Fig. 8 and 9 for typical RH sensor wiring.
S
J4- 1 or J4- 4 = 24vdc loop power
S
J4- 2 or J4- 5 = 4- 20mA signal input
NOTE
: The factory default for dehumidification control
is a normally open humidistat.
Installing Discrete Inputs
Compressor Safety
The compressor safety input provides the RTU Open with
feedback to when the compressor is not running and
should be. This feedback is usually provided by a
Compressor Lock-Out (CLO) device. Compressor safety
is a dedicated input on the configurable input 3 and tells
the RTU Open when the compressor is locked out. The
normal condition for compressor safety is good operation.
A normally open compressor safety is the factory default
for all units. Follow specific accessory instructions if
installing a CLO device. The CLO should wire into the
unit’s central terminal Board (CTB).
NOTE
: Input 3 can also be wired into J- 5.
SW2
1
2
3
4
5
6
ON
Io
Vin
Gnd
Vo
MOUNTING
HOLES
WIRING
OPENING
a33-9141
Vin - J4 -1 or J4 -4 24Vdc
Io - J4 -2 or J4 -5 4 -20mA output
C07201
Fig. 8 - Space Relative Humidity Sensor Typical Wiring
Humidistat
The accessory humidistat provides the RTU Open insight
to the relative humidity in the space. The humidistat reads
the RH level in the space and compares it to its setpoint to
operate a dry contact. The humidistat is a dedicated input
on the configurable input 9 and tells the RTU Open when
the RH level is HIGH or LOW. The normal condition for
humidity is LOW. A normally open humidistat is the
factory default control for the Perfect Humidity
t
option.
To wire in the field:
S
J5- 8 = 24 VAC source for dry contact
S
J5- 7 = Signal input
Single Enthalpy (Outdoor Enthalpy)
The outdoor enthalpy switch/receiver (33CSENTHSW)
senses temperature and humidity of the air surrounding
the device and calculates the enthalpy when used without
an enthalpy sensor. The relay is energized when enthalpy
is high (above 28 BTU/lb OR dry bulb temperature is
above 75
_
F) and de-energized when enthalpy is low
(below 27 BTU/lb AND dry bulb temperature is below
74.5
_
F). The enthalpy input is dedicated to input 8 and
tells the RTU Open when the outside air enthalpy is HIGH
or LOW. The normal condition for the enthalpy input is
HIGH. Enthalpy is configured on input 8 in the factory
when it is added as an option.
NOTE
:
The enthalpy calculation is done using an
average altitude of 1000 ft above sea level.
For field installation, refer to the enthalpy accessory
instructions. For wiring see below and Fig. 10. The RTU
Open board provides 24vac on one of the two loose grey
wires in the return air section of the rooftop near the
12-pin economizer plug. To determine the correct grey,
measure the voltage on the wires with power applied to
the unit. If 24-vac is sensed, then that is the grey wire that
is connected to the RTU Open board at J2-7. The other is
the signal for input 8, connect it to the LOW Enthalpy
terminal on the enthalpy switch/receiver. Tie into the
12-pin economizer plug on pin 4 or the black wire
connected to the actuator for the enthalpy’s GND
connection. Power can also be provided direct from the
unit transformer and J5 terminal on the RTU Open.
S
J2- 7 or J5- 2 = 24 VAC for enthalpy switch power
S
J2- 6 or J5- 1 = input signal
Differential Enthalpy
Differential enthalpy control requires both an enthalpy
switch/receiver (33CSENTHSW) and an enthalpy sensor
(33CSENTSEN). The enthalpy sensor must be installed in
the field as the factory can only provide single enthalpy.
The enthalpy sensor must be mounted in the return
airstream and calculates the enthalpy of the indoor air.
The relay is energized when the enthalpy detected by the
return air enthalpy sensor is less than the enthalpy at the
enthalpy switch/receiver. The relay is de-energized when
the enthalpy detected by the return air enthalpy sensor is
greater than the enthalpy at the enthalpy switch/receiver
(differential enthalpy control).
TS
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5580
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01